Tuesday, March 5, 2024

STRUCTURE OF A C PROGRAM

Beginning of C programming

  • BEGINNING OF A C PROGRAM
  • COMPILING OF A C PROGRAM
  • KEYWORDS AND IDENTIFIERS 
  • STATIC AND GLOBAL VARIABLE 
Let's understand the basic concepts of the language and its keywords by writing one small code

Let’s understand components and keywords in brief

Header file

The first line, or keyword, of a C Language program is #include<stdio.h>. The shared header data for the program, like as declarations, functions, and macro definitions, are included in (.h) files.

They are processed by the pre-processor, which the compiler calls.

Here are a few more typical applications for header files: -

A Stddef.h is useful for macros.

There is Stdint.h for integer types with precise widths.

See Stdio.h for basic input/output functions.

Functions for converting numbers, allocating memory, and generating pseudo-random numbers are included in Stdlib.h.

See String.h for functions that deal with strings.

See Math.h for commonly used mathematical functions.

 

Body of the method (enclosed in{})

 

The main manipulation will hold in the body part. It can be like anything as manipulations, searching, sorting, printing, etc.

The functions have to be in the braces.

 

Print statement (line 4)

 

Printf(“ hello world”);

This statement was given to the compiler and in C it is always terminated by ;(semicolon).

We use a function called printf() to display the typed text on the monitor as output.

 

Return statement

It is called the last section of the C program. This is a reference to the values that a function returns. These values and the function are dependent on the return type of the function such as main().

Maybe it is used by our OS to know the termination status of the program as 0 indicates the successful termination.

 

Compiling a C program

We already know that C language is a mid-level programming language that needs a compiler to execute code this compiler converts the code into a machine-level language that is then used by the machine to run.

In a simple language, we can easily understand it as 



In compilation, it converts the (.i) file into an assembled file (.s) containing assembly-level instructions.

An assembler is used to convert the (.s) assemble level code to machine-readable code like binary/hexadecimal code known as object code.

In Linking it integrates library files into the program. The linking process creates an executable file with an extension as (.exe) in DOS and (.OUT) in the Unix Operating system.

Q) what is an executable file?

An executable file is a set of files full of instructions encoded with sequence instructions that the system can execute directly as the user clicks on it and executes their program. It has many types of extensions like .exe, .bat, .com, .cmd, .inf, .ipa, etc.

EXE refers to an executable file, meaning that all EXE files are capable of being executed, whereas not all executable files are EXE.

Q) Using a terminal to run a very first program?

  


Q) what is a variable, and constant, and how to declare variables and naming conventions?

The combination of proper alphabets, numerals, and special symbols with constants, variables, and keywords. Let us understand what is a constant and a variable.

Let’s assume the variable is an empty container that contains any type of value that is being employed inside the program to resolve mathematical calculations. A variable name can have at most 31 characters, which means if we try to write a variable name with 32 then it will not be supported by C language.

The constant is a static entity that may not change its actual position. We can also state this as a variable is a container that contains the static values to solve the mathematical calculations.

Variety of C constants

a)       Primary constants

·       Integer constants

·       Real constants

·       Character constant

b)      Secondary constants

·       Array

·       Pointer

·       Structure

·       Union

·       Enum, etc.

Keywords and identifiers

C Programming keywords are specified, reserved words with specific meanings that are assigned by the compiler. Keywords cannot be used as identifiers because they are an essential part of the syntax. As an illustration:

Int city;

In this case, the keyword int designates that the variable money is an integer of type int.

Since the language C is case-sensitive, all keywords have to be written in lowercase. This is a list of all ANSI C-acceptable keywords.


 

IDENTIFIERS

The basic units of a program in the C programming language are called identifiers. Functions, variables, structs, and other entities are given unique names called identifiers. They serve as the entity's special identification within the program. In the example below, the string type value is identified as "section."

Rules for Naming Identifiers

While naming variables, a programmer must adhere to specific guidelines. The rules listed below must be adhered to for the identification to be valid.

Both numerals (0–9) and letters (a–z or A–Z) can be used as identification.

All that is permitted in identification is the underscore '_'.

You cannot use spaces while naming as an identifier.

Only letters or an underscore may start an identifier.

Since identifiers are words that are reserved for a particular purpose, we cannot name them similarly to keywords. Printf, scanf, int, char, struct, etc. are a few examples. If we try to use a keyword's name as an identifier, the compiler will throw an error.

Within its namespace, the identification needs to be unique.

Because C is a case-sensitive language, "name" and "NAME"

Static variable and global variable

Variables defined outside of the function are referred to as global variables. Global variables have an end-of-file or program scope, which starts at the moment of formation. a result of their external linkage, references to the same memory address in different source files.

Static global variables do not clash with other variables of the same name in other source files because they are specific to the source file in which they are defined.

Both static and global variables have static initialization, which implies that in cases where you don't set a value for them, NULL (for pointers) or 0 (for common variables) will be provided.

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